In a Digital Video Disc (DVD) for read-only disk type application, packetized video data, conforming to the Motion Picture Expert Group #2 (MPEG-2) standard for compression, and/or audio data are multiplexed onto a DVD disc. The data are recorded in a manner compliant with Part 3, VIDEO SPECIFICATIONS of the existing DVD Specifications for Read-Only Disc (the Specification). The read-only DVD data format employs a sub-set of the MPEG-2 format and is defined by a proprietary standard adopted by a consortium of consumer electronics companies and described in available literature such as “DVD Demystified—The Guidebook of DVD-Video and DVD-ROM”, 1997, by Jim Taylor published by McGraw Hill. Further, MPEG-2 compatible data is encoded in accordance with the “MPEG standard” comprised of a system encoding section (ISO/IEC 13818-1, 10th Jun. 1994) and a video encoding section (ISO/IEC 13818-2, 20th Jan. 1995).
Multiplexed data are segmented into logical blocks referred to as Video Object Units (VOBU's) forming a presentation sequence. FIG. 1 illustrates schematically a normal forward presentation sequence that includes, for example, VOBU (n−m), VOBU(n) and VOBU (n+m) in that order. The number represented by the symbol “n” provides the position of the VOBU within the sequence. Current VOBU (n) represents, for example, the VOBU that currently provides the video and audio information for playback or for recording, in accordance with the context. Similarly, future
VOBU(n+m) provides the video and audio information following current VOBU (n) and is separated from current VOBU (n) by a number of intervening VOBU's determined by the numerical value of the symbol “m”. In the same manner, past VOBU (n−m) provides the video and audio information prior to current VOBU (n).
FIG. 2 illustrates schematically the data structure within VOBU (n). Similar symbols and numerals in FIGS. 1 and 2 indicate similar items or functions. The video information of VOBU (n) of FIG. 2 is encoded in accordance with the MPEG-2 standard and recorded in data fields, each occupying a single sector on the disc, for example, a data field or portion Video Pack (V-PCK) 202. Similarly, audio information is recorded in data fields, each occupying a single sector on the disc, for example, a data field or portion Audio Pack (A-PCK) 203.
Additionally, the data structure of VOBU (n) includes a single data field or portion Navigation Pack (Nav_Pack) 201, containing information concerning the presentation control of VOBU (n) and occupying a single sector on the disc. Data field Nav_Pack 201 includes a data field referred to in the specification as Data Search Information (DSI), not shown, that includes a data field VOBU Search Information (VOBU—SRI) 201a having a length of 168 bytes. Field VOBU—SRI 201a contains information selectively used for searching data in either future or past VOBU's relative to current VOBU (n) in order to perform “trick” play operation such as fast reverse or fast forward. In the trick play operation, a sub-set of the pictures VOBU's in the presentation sequence provide content information for achieving a look that is faster than in the normal presentation sequence.
The table of FIG. 3 includes FIGS. 3A and 3B. A given 4-byte address pointer or data word FWDI(m), shown in the table of FIG. 3 and contained in field VOBU—SRI 201a of current VOBU (n) of FIG. 1, identifies a start, logical sector address of a corresponding future VOBU, not shown, associated with data word FWDI(m). Similar symbols and numerals in FIGS. 1, 2 and 3 indicate similar times or functions. In normal forward presentation mode, a future VOBU such as, for example, future VOBU (n+m), associated with data word FWDI(m) is presented for display, following an interval measured from the presentation start time of current VOBU (n) that has a duration, in seconds, equal to 0.5 multiplied by the value of “m”. The parameter “m” is selected from the consecutive integer values, 1 through 15 and the integer values 20, 60, 120 and 240. For example, word FWDI(m=20) refers to a future VOBU which is presented in the normal forward presentation sequence 20 VOBU's following current VOBU (n).
Similarly, each 4-byte address pointer or data word BWDI(m) in the table of FIG. 3 identifies the start, logical sector address of a corresponding past VOBU, for example, VOBU (n−m), associated with data word BWDI (m). The past VOBU associated with data word BWDI (m) is presented for display, in normal forward presentation mode, before the presentation start time of current VOBU (n) by an interval having a duration, in seconds, equal to 0.5 multiplied by the value of “m”. The parameter “m” can be selected from the same integer values. For example, word BWDI(m=20) refers to a VOBU which appears is in the presentation sequence 20 VOBU's before current VOBU (n).
In a trick mode operation, a DVD player, not shown, conforming to the Specification, may obtain the address of the next VOBU for processing from the corresponding entry, word FWDI(m) or BWDI(m), in field VOBU—SRI 201a of current VOBU (n) of FIG. 2. Thereby, the presentation of the video information contained in intervening VOBU's is omitted or skipped over to provide for fast forward or fast reverse trick mode operations. For example, when, in the fast trick mode the 21th future VOBU is presented immediately after current VOBU (n), the presentation of the 20 VOBU's, interposed between them, are skipped over. When displaying 1-only pictures for 10 fields per 1 picture, the result is a fast trick mode operation that is approximately 60 times faster than in the normal presentation mode.
It may be desirable to perform a real-time recording of audio and video content on discs compatible for playback operation with existing read-only DVD players, intended for discs conforming to the Specification. That means that data words FWDI(m) and BWDI(m) have to be provided in the data stream. Recording data words BWDI(m) in current VOBU (n) does not necessitate the usage of a large buffer memory in the recorder. This is so because the sector addresses of past VOBU's associated with data words BWDI(m) could be computed prior to receiving the data of current VOBU (n).
On the other hand, accumulating appropriate values for recording data word FWDI (m) might, disadvantageously, require a large buffer memory. Because of a variable bit-rate in MPEG encoding, without extensive data buffering, it cannot be known at the time the video data, for example, of current VOBU (n) is produced by the MPEG encoder what addresses the future VOBU will have.
In order to record in field VOBU—SRI 201a, for example, word FWDI(m=240) of FIG. 3, related to the 241th future VOBU, all the video information of the intervening VOBU's has to be encoded, assembled and stored for computing the starting sector address of the 241th future VOBU. The 241th future VOBU appears 240 VOBU's after current VOBU (n). Therefore, the information associated with each of the intervening 240 future VOBU's might have to be stored in a memory prior to recording on the disc the information of field VOBU—SRI 201a of current VOBU (n). After each of the 241 future VOBU's has been produced, words FWDI(m) of the table of FIG. 3 could be generated. Disadvantageously, storing such a large number of VOBU's requires an excessively large storage space in the memory in the range of 100 Mega-Byte.
In carrying out an inventive feature, the address pointer for each of the 61th, 121th and 241th future VOBU's, ahead of current VOBU (n) of FIG. 1, that, according to the Specification, should be contained in words FWDI(m=60), FWDI(m=120) and FWDI(m=240), respectively, instead, is set to a value that need not conform to the Specification. Whereas, the address contained in each of words FWDI(m=1) through FWDI(m=20) is made to conform to the Specification. Consequently, the maximum fast forward trick mode, that corresponds to word FWDI(m=20), is 60 times faster than in the normal presentation mode, as indicated before. Advantageously, such an arrangement reduces the memory requirement significantly, to the order of 8 Mega-Byte.
In carrying out a further inventive feature, in each of words FWDI(m=60), FWDI(m=120) and FWDI(m=240), respectively, the value of, for example, word FWDI(m=20) associated with the 20th future VOBU is, instead, recorded. Thereby, a DVD player having the capability of operating in a fast forward trick mode, faster than 60 times the normal presentation mode, will be limited to the 60 times faster trick mode.
The logical sector addresses provided in field VOBU—SRI 201a are valid, in accordance with the Specification, for a predetermined group of VOBU's referred to as a “Cell” such as Cell 206 of FIG. 1. Cell 206, for example, is a logical association of VOBU's that includes, for example, VOBU (n−m), VOBU (n) and VOBU (n+m), and the intervening VOBU's. Cell 206 is delineated by two sector addresses containing a start logical sector number and an end logical sector number, respectively. In the Specification, Section 4.5.4, subsections 2 and 4, it is stated that if a given word FWDI (or BWDI) were to point to an address of a VOBU outside the range of a Cell, such as Cell 206, then, instead, it should contain a bit combination referred to as “does not exist” code, rather than an address pointer of an actual VOBU.
In accordance with another inventive feature, each Cells is constrained in size to only 59 VOBU's. As a result of constraining each Cell in size to only 59 VOBU's, the entries for each of words FWDI(m=60), FWDI(m=120) and FWDI(m=240) need only contain the aforementioned “does not exist” code. Therefore, advantageously, the need for a large buffer memory is diminished.